Security surveillance systems are very widely used in areas, where surveillance is necessary, such as factories, dormitories, stores, entrances of buildings and community housings, or secret and hidden places, where people rarely go, so that the security surveillance systems may make recording of instantaneous image information by means of transmitter modules and receiver modules thereof (including lighting modules and imaging systems).
A common problem of using the security surveillance system in nighttime is that lighting is insufficient and the image gets unclear and blurring. The security surveillance system is often built in with a lighting module including an infrared light-emitting diode or an infrared laser source in order to allow the imaging system to acquire a clear image thereby allowing the security surveillance system to carry out effective surveillance even in a light-insufficient area. However, a regular light-emitting diode or laser source usually generates a light shape that is an isotropic circular-symmetry light shape, in which light intensity in a central zone is far greater than that at a peripheral zone so that an edge of an image becomes relatively dark with inhomogeneous lighting brightness, whereby the security surveillance may not retrieve clear image information of an object located in the peripheral zone of an acquired image.
Referring to FIG. 14a, which is a schematic view illustrating image information acquired with a conventional surveillance camera device, a regular light-emitting diode or laser source usually generates a light shape that is a circular-symmetry light shape, in which light intensity in a central zone is often far greater than that at a peripheral zone so that the camera cannot clearly photograph an object located in the peripheral zone of an imaged area. Thus, a dark zone A appears in the peripheral zone of the image information. For instance, FIGS. 16a to 16d show a variety of the half-power view angles of the circular-symmetry light shape (which is a light angle that light intensive value is half of the intensive value of the axis direction) of the light receiving plane homogeneity diagrams, wherein the half-power view angles are 120, 90, 60 and 45 degrees in sequence, which shows the light are centralized in the center portion.
Referring to FIG. 14b, which is another schematic view illustrating image information acquired with a conventional surveillance camera device, to match a specific image aspect ratio (such as 4:3) acquired with the camera, a known lens mechanism usually has a rectangular opening. This arrangement may lead to a great loss of optical energy E and results in poor coverage so that an image of a photographed object is trimmed by the rectangular opening, causing distortion of a portion of the image.
Thus, to improve object image information retrieved from the peripheral zone by the security surveillance system, the known designs of the security surveillance systems often involve a large number of lighting modules, such as infrared light-emitting diodes and infrared laser sources to enhance brightness for optical lenses, or more than one optical devices are used, such as optical lenses or reflectors, in order to conduct optical adjustment through reflection and refraction of light to thereby enhance clarity and sharpness of a surveillance image, wherein air or other filling materials that are different from the materials of the optical devices are present between the optical devices and the lighting modules. Such optical devices are so called secondary optical devices. As shown in FIG. 15, which is a schematic view illustrating a known surveillance camera device mounted to a ceiling, the known camera device 5 is attached to a ceiling 6 and the camera device 5 comprises a casing 51, an image capturing element 52, and at least one light supplementing structure 53. The light-supplementing structure 53 comprises a light reflector 531 and a light emission module 532 and uses multiple reflection surfaces 5311, 5312 of the light reflector 531 to convert, through light reflection, circular-symmetry light generated by the light emission module 532 to generate a special light shape fit to the camera device 5 so as to increase illumination on the ceiling 6 and in an area under the ceiling 6 and to enhance clarity of an image captured by the image capturing element 52 thereby eliminating the problem that no high quality image can be acquired by the camera device 5 due to insufficient illumination. However, such an arrangement still suffers the following problems:
(1) Since the secondary optical arrangement uses reflection and refraction of light to generate non-symmetric light shape, the overall lighting efficiency deteriorates due to multiple times of reflection and refraction of light. During an operation of the surveillance device in nighttime, in order to meet the illumination required for nighttime imaging, the illumination must be increased due to loss caused by multiple time of reflection and refraction and thus, power consumption of the security surveillance system becomes excessively high.
(2) Although design difficulty of a secondary optical arrangement is low for there are multiple optical design parameters involved, yet positional shift may readily occur during an assembly process of the optical elements and the light emission modules. In addition to difficulty of assembly and increased manufacturing cost due to complicated parts involved, the size of the surveillance camera device may get bulky so that thinning and miniaturization are not possible.
Thus, it is one of the issues that need to be overcome by those devoted themselves in research and study in this field to increase illumination, homogeneity, and coverage of a surveillance camera in order to acquire excellent imaging result and also to lower down power consumption and reduce the size of the surveillance camera.